Audio devices including, without limitation, wireless telephones and media players are in widespread use and are often used with headphones or earbuds including a loudspeaker that produces an audible output. The audio performance of such devices with respect to intelligibility can be improved with noise cancelling using one or more noise cancellation microphones to measure ambient noise and then using signal processing to generate an anti-noise signal and combine it with an audio signal provided to the loudspeaker. Noise cancelling may include the use of a noise cancellation microphone referred to herein as an error microphone, for sensing a combination of speaker output and ambient noise near a listener's ear drum. Noise cancelling may also include a second noise cancellation microphone referred to herein as a reference microphone, for sensing undesired ambient noise in order to remove or offset the ambient noise and any other undesired components from the audible output of the speaker.
Locating one or more noise cancellation microphones within a small media player or wireless telephone or within an even smaller headphone, headset, earbud, or other earpiece, is generally challenging due to confined spaces inherent in such devices. It may be even more difficult to locate different types of noise cancellation microphones at the optimal locations. For example, it may be difficult to mount an error microphone at or near the acoustical output of a speaker. More generally, it may be difficult to locate one or more acoustic sensors or transducers within an audio device or a headphone or other earpiece.